What Is Haemophilus Influenza Type B (Hib)?

Haemophilus influenza (H. influenzae) is a bacterial infection that was erroneously first identified in 1892 as the cause of influenza. It was later determined to be an invasive bacterial infection that is exclusively a human pathogen spread by airborne droplets through sneezing or coughing, or by direct contact with secretions or fomites. Six major serotypes of H. influenzae have been identified and labeled with the letters a through f. Some strains, which don’t have a polysaccharide capsule, are still untyped.

Invasive H. influenza type b (Hib) can cause severe illness, including meningitis and systemic, invasive disease in the bones and joints. Invasive means that germs spread to other parts of the body. Hib is mostly found in infants and children under 5 to 6 years old. However, nontypable strains of H. influenzae can also be found in humans, particularly in the upper respiratory tracts of up to three-fourths of all healthy adults. The nontypable strains can cause otitis media in infants and children and lower respiratory tract infections in adults with chronic bronchitis. However, the incidence of invasive disease caused by nontypable strains is low.1,2

For infants and children under age 6, the most common types of invasive disease caused by Hib are meningitis, epiglottitis, pneumonia, arthritis, and cellulitis. Meningitis is an infection of the membranes covering the brain and spinal cord, and Hib was responsible for 50 to 65 percent of meningitis cases before the vaccine was introduced in the mid-1980s. Other causes of meningitis in infants and children are Neisseria meningitides and Streptococcus pneumoniae. Symptoms of Hib meningitis are fever, decreased mental status, and stiff neck.

Epiglottitis is an infection and swelling of the epiglottis, and can cause life-threatening airway obstructions. Septic arthritis (joint infection), cellulitis (rapidly progressing skin infection usually involving the face, head, or neck, and pneumonia, mild or severe, are also caused by Hib. Bone infections (osteomyelitis) and pericarditis are less common forms of the disease.3

The most common symptoms of severe Hib infection are fever and altered central nervous system function. Less common symptoms can be osteomyelitis, septic arthritis, pericarditis, orbital cellulitis, endophthalmitis, urinary tract infection, abscesses, and bacteremia.4

NVIC encourages you to become fully informed about Haemophilus Influenza Type B (Hib) and the Hib vaccine by reading all sections in the Table of Contents , which contain many links and resources such as the manufacturer product information inserts, and to speak with one or more trusted health care professionals before making a vaccination decision for yourself or your child. This information is for educational purposes only and is not intended as medical advice.